Total bridges
109
Public highway bridges in Boone County
County profile · official public datasets
Boone County, IL
109 public highway bridges tracked in the FHWA National Bridge Inventory: 56% rated Good, 37.6% Fair, 6.4% Poor.
- 109
- Public bridges
- 56%
- Good condition
- 6.4%
- Poor condition
The verdict
According to the Federal Highway Administration's 2024 National Bridge Inventory.
Boone County pairs a better-than-median Poor-condition share among rated counties in the state with a newer average build year than the state inventory.
- Top 33%
- lowest Poor share in state
- 6.4%
- Poor-condition share
- 109
- public highway bridges
- 1986
- avg year built
Poor is an FHWA condition category from the lowest applicable component rating (4 or below), not a live crossing-safety or closure decision. Rankings cover counties with at least five public highway bridges.
Boone County Bridge Snapshot
According to the Federal Highway Administration's 2024 National Bridge Inventory, Boone County ranks #34 of 102 Illinois counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 6.4%). Boone County, Illinois contains 109 public highway bridges. Roughly 56% are rated “Good,” 37.6% “Fair,” and 6.4% “Poor.” Poor means the lowest applicable deck, superstructure, substructure, or culvert rating is 4 or below on the 0–9 NBI scale. It is a condition category, not a live safety or closure decision.
Responsible agencies inspect covered bridges on risk-based intervals under current NBIS rules and submit inventory data to FHWA annually. The list below shows every NBI-tracked bridge in the county. Use the “Sort by” controls to change the ordering, and click any row for its reported inspection date, traffic count, and condition fields.
Source: FHWA National Bridge Inventory. See methodology for full definitions.
Good condition
56%
61 of 109 rated 7-9
Fair condition
37.6%
41 of 109 rated 5-6
Poor condition
6.4%
7 of 109 rated 4 or below
In-state Poor-share rank
#34 of 102
Among Illinois counties with 5+ bridges, lower share ranks better
Condition distribution
Share of 109 NBI-tracked bridges by lowest applicable component rating.
Good 56% (61)
Fair 37.6% (41)
Poor 6.4% (7)
Boone County's Poor-condition bridges carry 16,325 vehicle crossings a day
That is 3.6% of the county's reported daily bridge traffic on 6.5% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 2,332 crossings a day against 4,325 for a Good-condition one. A Poor rating is a condition category, not a closure or a live safety judgement; it means the lowest applicable component rating is 4 or below.
Computed over the 108 of 109 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.
36.7% of Boone County's bridges have passed the 50-year mark
40 of the 109 bridges with a recorded construction year were built in 1974 or earlier. Age alone is not a defect: a well-maintained older bridge can rate Good, and 56% of this county's inventory does. Even so, this older cohort is the population from which future Poor ratings are drawn, which is why the age profile below matters alongside the condition split above.
Cutoff derives from the 2024 release year minus a 50-year design life. Source: FHWA National Bridge Inventory, 2024 release.
One structure carries 71.7% of the county's Poor-condition bridge traffic
S. APPLETON ROAD over KISHWAUKEE RIVER, built 1964, carries 11,700 vehicles a day, the most of any Poor-rated structure here. The county's Poor-condition exposure is concentrated rather than evenly spread, so the 7-bridge count understates how much of the daily burden sits on a single crossing.
Share is of the 16,325 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.
When Boone County's bridges were built
109 bridges with a recorded construction year, grouped by decade
- 1900s 1
1900–1909
1 bridges
- 1940s 1
1940–1949
1 bridges
- 1950s
1950–1959
15 bridges
- 1960s
1960–1969
15 bridges
- 1970s
1970–1979
15 bridges
- 1980s
1980–1989
13 bridges
- 1990s
1990–1999
12 bridges
- 2000s
2000–2009
11 bridges
- 2010s
2010–2019
22 bridges
- 2020s 4
2020–2029
4 bridges
What this shows Construction peaked in the 2010s, when 22 of the county's bridges still in the inventory were built, which is 20.2% of those with a recorded year. That cohort is now 5 to 14 years old in the 2024 inventory. Its average build year is 1986, 7 years newer than the Illinois average of 1979.
How Boone County compares with Illinois's closest counties by inventory size
The 5 Illinois counties nearest Boone County in number of bridges, with their condition splits. Its 6.4% Poor share is the 3rd-lowest of these 6. Its average build year of 1986 against a peer-group mean of 1981 is 5 years newer.
Showing the 5 closest of 101 Illinois counties eligible for comparison.
| County | Bridges | Good | Fair | Poor | Avg. built |
|---|---|---|---|---|---|
| Johnson County | 118 | 58.5% | 39% | 2.5% | 1979 |
| Schuyler County | 114 | 21.1% | 68.4% | 10.5% | 1981 |
| Jersey County | 113 | 57.5% | 38.1% | 4.4% | 1981 |
| Boone County (this page) | 109 | 56% | 37.6% | 6.4% | 1986 |
| Pulaski County | 108 | 35.2% | 56.5% | 8.3% | 1981 |
| Scott County | 99 | 54.5% | 38.4% | 7.1% | 1983 |
Each share is of that county's own total tracked bridges; peers are the counties with 5 or more bridges whose inventory size is closest to Boone County's. Source: FHWA National Bridge Inventory, 2024 release.
Nationwide counties with similar inventory size or average build year
Two NBI-derived peer sets for Boone County, both outside Illinois so the neighborhoods are not the same-state size table above.
Similar inventory size
Nearest county inventories outside IL (109 bridges here).
- Mariposa County, CA · 109 bridges
- Gove County, KS · 109 bridges
- Hodgeman County, KS · 109 bridges
- Trigg County, KY · 109 bridges
Similar average build year
Nearest mean year-built outside IL (1986 here).
- El Paso County, TX · avg 1986 · 783 bridges
- Caddo County, LA · avg 1986 · 682 bridges
- Weld County, CO · avg 1986 · 614 bridges
- Polk County, IA · avg 1986 · 545 bridges
Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.
Fair-condition bridges (41)
SQUAW PRAIRIE RD
FairOver: BEAVER CREEK
2.5 MI NW BELVIDERE, Boone, IL
Built 1959 Load: 18.5 t ADT: 1,650
WOODSTOCK RD
FairOver: PISCASAW CREEK
.6 MI E POPLAR GR RD, Boone, IL
Built 1957 Load: 20.4 t ADT: 1,800
RUSSELLVILLE RD
FairOver: PISCASAW BRANCH
5.0 MI SE POPLAR GR, Boone, IL
Built 1960 Load: 21.7 t ADT: 700
MARENGO RD
FairOver: PISCASAW CREEK
1.5 MI NE BELVIDERE, Boone, IL
Built 1965 Load: 24.0 t ADT: 2,200
DAWSON LAKE RD
FairOver: BRANCH OF BEAVER CR
5.0 MI N BELVIDERE, Boone, IL
Built 1958 Load: 24.3 t ADT: 1,750
BERGEN RD
FairOver: N KINNIKINNICK CREEK
7.5 MI NW POPLAR GRV, Boone, IL
Built 1989 Load: 24.3 t ADT: 10
N BOONE SCHOOL RD
FairOver: S. KINNIKINNICK CRK.
3.0 MI N CALEDONIA, Boone, IL
Built 1965 Load: 24.3 t ADT: 100
SHATTUCK RD
FairOver: MOSQUITO CREEK
3.0 MI E BELVIDERE, Boone, IL
Built 1958 Load: 24.6 t ADT: 750
GUSTAFSON RD
FairOver: BEAVER CREEK
3.5 MI NW BELVIDERE, Boone, IL
Built 1958 Load: 25.9 t ADT: 125
S. APPLETON ROAD
FairOver: KISHWAUKEE RIVER
S OF LINCOLN AVE, Boone, IL
Built 1964 Load: 27.9 t ADT: 11,700
ILL ROUTE 173
FairOver: BEAVER CR TRIBUTARY
1.5 MI W CAPRON, Boone, IL
Built 1974 Load: 31.1 t ADT: 4,550
IL 76
FairOver: DRAINAGE DITCH
0.8 MI. N.OF BUS 20, Boone, IL
Built 1994 Load: 32.4 t ADT: 10,300
NEWBURG RD
FairOver: KISHWAUKEE RIVER
3.5 MI W OF BELVIDER, Boone, IL
Built 1962 Load: 32.4 t ADT: 8,050
MCCURRY RD
FairOver: N KINNIKINNICK CREEK
5.5 MI NE ROSCOE, Boone, IL
Built 1967 Load: 32.4 t ADT: 150
N BOONE SCHOOL RD
FairOver: BEAVER CREEK
2.5 MI NW CAPRON, Boone, IL
Built 1957 Load: 32.4 t ADT: 200
RUSSELLVILLE ROAD
FairOver: PISCASAW CREEK
1.5 M SE POPLAR GROV, Boone, IL
Built 1980 Load: 32.4 t ADT: 650
CAPRON RD
FairOver: BR PISCASAW CREEK
3.5 MI S CAPRON, Boone, IL
Built 1981 Load: 32.4 t ADT: 150
BEAVERTON ROAD
FairOver: BEAVER CREEK
1.0 M E POPLAR GROVE, Boone, IL
Built 1983 Load: 32.4 t ADT: 375
EPWORTH RD
FairOver: KISHWAUKEERIVER
3.MI E OF BELVIDERE, Boone, IL
Built 1985 Load: 32.4 t ADT: 450
RIVERSIDE ROAD
FairOver: BEAVER CREEK
4.0 MI NW BELVIDERE, Boone, IL
Built 1988 Load: 32.4 t ADT: 2,350
SPRING CREEK RD
FairOver: BEAVER CREEK
4 MI NW OF BELVIDERE, Boone, IL
Built 1993 Load: 32.4 t ADT: 4,300
WHEELER RD
FairOver: CN RR
2 MI N DEKALB CO LN, Boone, IL
Built 1998 Load: 32.4 t ADT: 200
IL 173
FairOver: BEAVER CREEK
0.5 MI. SW. CAPRON, Boone, IL
Built 1994 Load: 33.0 t ADT: 4,550
US 20
FairOver: COON CREEK
2 MI. E. BELVIDERE, Boone, IL
Built 1996 Load: 33.7 t ADT: 8,550
POPLAR GROVE RD
FairOver: US 20 BR
NE OF BELVIDERE, Boone, IL
Built 1986 Load: 34.0 t ADT: 3,600
HUBER ROAD
FairOver: MOSQUITO CREEK
3.5 MI SE BELVIDERE, Boone, IL
Built 1977 Load: 34.7 t ADT: 150
IL 173
FairOver: BEAVER CREEK
2.0 MI E POPLAR GROV, Boone, IL
Built 2008 Load: 36.6 t ADT: 4,550
SQUAW PRAIRIE RD
FairOver: PISCASAW CREEK
2.0 MI NE BELVIDERE, Boone, IL
Built 1978 Load: 37.6 t ADT: 1,350
US 20 BR
FairOver: BEAVER CREEK
2.5 MI W BELVIDERE, Boone, IL
Built 1957 Load: 38.9 t ADT: 13,400
US 20 BR
FairOver: TRIB. OF BEAVER CR.
.1 MI E. WINN. CO LN, Boone, IL
Built 1989 Load: 38.9 t ADT: 13,400
MAIN ST
FairOver: KISHWAUKEE RIVER
S OF LINCOLN AVE, Boone, IL
Built 1972 Load: 39.5 t ADT: 4,150
US BR 20
FairOver: KISHWAUKEE RIVER
E EDGE OF BELVIDERE, Boone, IL
Built 1986 Load: 39.9 t ADT: 11,100
Garden Prairie Roa
FairOver: I-90
1 Mi W. of Co. Line, Boone, IL
Built 2015 Load: 44.4 t ADT: 150
US 20 EB
FairOver: I-90
.11 MI E WHEELER RD, Boone, IL
Built 1964 Load: 46.7 t ADT: 14,200
US 20 WB
FairOver: I-90
.13 MI E WHEELER RD, Boone, IL
Built 1958 Load: 48.3 t ADT: 14,200
US 20 EB
FairOver: S APPLETON RD
SW EDGE BELVIDERE, Boone, IL
Built 1966 Load: 51.2 t ADT: 13,100
IL 76
FairOver: BEAVER CREEK
2.5 MI. S. IL 173, Boone, IL
Built 1990 Load: 51.8 t ADT: 8,250
US 20 WB
FairOver: S APPLETON RD
SW EDGE BELVIDERE, Boone, IL
Built 1966 Load: 60.3 t ADT: 13,700
COUNTY LINE RD
FairOver: MUD CREEK
8.0 MI NE BELVIDERE, Boone, IL
Built 1959 Load: 72.9 t ADT: 675
HUNTER ROAD (FAS 3
FairOver: BR OF S KINNIKINNICK
0.2 MI E OF CO LINE, Boone, IL
Built 1975 Load: 80.0 t ADT: 2,150
LEROY CENTER RD
FairOver: BEAVER CREEK
3.0 MI NW CAPRON, Boone, IL
Built 1968 Load: 88.8 t ADT: 10
Read our methodology - how this data is sourced, computed, and verified.
Related
Data sourced from official public datasets. See our methodology for details. Retrieved and formatted by PlainBridges
Every figure on PlainBridges is rendered directly from federal source data, no number is typed in by an editor. This page draws directly on federal source data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. NBI condition categories reflect the latest reported inventory record, not a live safety, closure, or travel decision.